Load testing isn't quite the expensive proposition it seems!
Think about it - clients or requests are really just ephemeral ports...
There are something like 30 thousand of them available by default with Linux
If you use sockets you can have as many connections as your system allows for open file descriptors. The upward limit is...
$ sysctl fs.file-max
fs.file-max = 9223372036854775807
Spawn a ton of concurrent requests to hit the service/API!
apachebench is a decent example of the idea; imagine some proprietary sauce with it
It gets cheaper (and in some ways, more effective) if you actually remove the network -- latency goes down
You can also rate limit it in software, but it's really not analogous in some ways (eg: net.core.somaxconn limitations/realities)
Development time is totally understandable though. It's important I leave my green field of comfort